It's that way with any 'special interest group'. They see it as them versus the world.
We know from history that the 'priest class' was quick to use their power against the people, all the while proclaiming their holiness and morality.
Ditto the Catholic church. I'm actually worried for the life of the first good Pope we've had for a while. (the predecessors weren't necessarily bad, just ineffectual). Ask anyone who is among the most corrupt in Italy and they'll say 'the Vatican'.
Cops are no different. THey've gotten power and will do anything to keep it, even subvert their mission. And like most people who do evil acts, don't see themselves as 'evil', just misunderstood.
The Sergeant on the recent case of the young thug who hit this old lady as she walked out of a store and youtubed it said she thought it was just harassment. OMG, they have the kid on tape smacking this old lady in the head. Yes he had a snowball in his hand, but he hit her in the head - there was no 'snowball throwing'. Yet the female cop said it wasn't 'substantial injury' and couldn't be prosecuted. On tape, hit to the head, a crime against the elderly and she feels it's ok. Bet she wouldn't do that if it was HER grandmother.
We're like a group of Diogenes with lamps of the 2nd and 4th Amendment looking for an honest cop. Good luck, fellas, you ain't finding one.